Hey there! While I can't comment on the fastapi portion of the question, our documentation for Passenger tools can be found here:
docs.cpanel.net
If the app itself works properly in passenger, I would expect it to be able to be used through that interface.
Application Manager | cPanel & WHM Documentation
This interface allows you to deploy applications with the Phusion Passenger® application server.
docs.cpanel.net
If the app itself works properly in passenger, I would expect it to be able to be used through that interface.